The often-disabling diarrhea associated with HIV infection reflects pronounced insults to intestinal epithelium. The purpose of this protocol is twofold: (1) to define comprehensively the pathophysiologic alterations in epithelial function in HIV-related diarrhea, and (2) to ascertain the effects of glutamine-based oral rehydration, vitamin A supplementation, or the combination of the two on both diarrhea rates and sensitive measures of epithelial function.